The Bauschinger Effect describes material weakening due to plastic deformation followed by load reversal. In expanded casings, this occurs when the casing is first expanded and when later during operation of the well the pressure comes from the outside (formation pressure, pressing salt formations or other). Expansion creates tensile stress in a circumferential direction, whereas the outside pressure which the casing has to withstand during operation of the well creates compressive stress in the circumferential direction. This is the nature of the load reversal on the tubular after expansion as compared to during expansion. The expanded casing or tubular loses up to 30% or more in compressive yield strength and up to 20% or more in modulus of elasticity (or E-Mod.). The Bauschinger Effect can be compensated with heat treatment at temperatures of 150 to about 300° C. or more for several hours. Bauschinger Effect compensation results in the expanded tubular material regaining some of its initial compressive yield strength and E-Mod. Full Bauschinger compensation means that the material regains its strength and elasticity as they were before the expansion.
The present invention uses an exothermic chemical reaction between one liquid and another substance which may be fluid or solid or other material. The reactants can be pumped into the borehole where they react and create heat. Long casing sections can be treated at the same time. Keeping the reactants apart from one another prior to the reaction may be done in different ways, including but not limited to, pumping two fluid columns separated by a spacer fluid. The heat which is created by this reaction can be used to compensate the Bauschinger Effect. The heat can also be used to aid and speed up cement curing. Faster cement curing maybe of interest in any kind of cemented tubular, whereas Bauschinger Effect compensation is only of interest in expandable tubulars. The minimum temperature for Bauschinger Effect Compensation is between about 150 and about 300° C.
US Publication 2011/0114323A1 teaches chemical exothermic reactions for treatment of oilfield deposits. The patent application describes reactions which reach temperatures up to 245° C. In general chemical reactants and procedures which are used for removal of oilfield deposit may be applicable to compensation the Bauschinger Effect as well. Other references relating to using exothermic reactions to remove paraffin deposits are U.S. Pat. Nos. 4,755,230 and 5,484,488.
In other contexts, references that address the Bauschinger effect in pipe manufacturing for downhole applications are:                US Publication 20080286504 Steel Plate or Steel Pipe with Small Occurrence of Bauschinger Effect and Methods of Production of Same;        U.S. Pat. No. 7,818,986 Multiple Autofrettage; U.S. Pat. No. 7,459,033 Oil Country Tubular Goods Excellent in Collapse Characteristics After Expansion and Method of Production Thereof;        US20050217768 Oil Country Tubular Goods Excellent in Collapse Characteristics After Expansion and Method of Production Thereof;        US Publication 20090320965 UOE Steel Pipe Excellent in Collapse Strength and Method of Production Thereof;        U.S. Pat. No. 7,967,926 UOE Steel Pipe Excellent in Collapse Strength and Method of Production Thereof;        U.S. Pat. No. 7,892,368 UOE Steel Pipe Excellent in Collapse Strength and Method of Production Thereof;        US Publication 20050178456 UOE Steel Pipe with Excellent Crash Resistance, and Method Of Manufacturing the UOE Steel Pipe;        U.S. Pat. No. 7,575,060 Collapse Resistance of Tubing;        U.S. Pat. No. 4,772,771 Method for the Production of High Strength Electric Seam Welded Oil-Well Pipe;        US Publication 20100119860 Steel Pipe Excellent in Deformation Characteristics and Method of Producing the Same;        US Publication 20090092514 Steel Pipe for High Strength Line Pipe Superior in Strain Aging Resistance and Steel Plate for High Strength Line Pipe and Methods Of Production of the Same;        US Publication 20100038076 Expandable Tubulars for Use in Geologic Structures.        
What is needed and provided by the present invention is a way to counteract the Bauschinger effect after the tubular sting is expanded in the subterranean location and preferably before the string is compressively loaded. Another advantage of the present invention can be the acceleration of the curing time for cement or other temperature sensitive material for curing whether the sealant is placed before or after tubular expansion. In the preferred embodiment an exothermic chemical reaction is made to occur within the expanded tubular while the expanded tubular wall is protected from differential loading that causes compressive stress in the tubular wall. This stress management can be accomplished with variation of mud densities within the expanded string. Reactants can be delivered while separated with a buffer fluid or another barrier that degrades or disappears over time. The exothermic nature of the reaction raises the tubular temperature for a sufficient time and to a required temperature so that the tubular material regains its yield strength lost in the expansion or a portion thereof as well as its modulus of elasticity. If cement or other sealant has been placed in the wellbore about the expanded tubular, either before or after the expansion, the heat generated also accelerates the curing time of the cement used in either a single wall or dual wall strings. Those skilled in the art will more readily appreciate these and other aspects of the present invention by a review of the detailed description of the preferred embodiment with the associated drawings while appreciating that the full scope of the invention is to be determined from the appended claims.